Double-metal cyanide catalysts for preparing polyether polyols

ABSTRACT

The invention relates to double-metal cyanide (DMC) catalysts for preparing polyether polyols by the polyaddition of alkylene oxides on to starter compounds containing active hydrogen atoms, wherein the DMC catalysts are composed of: a) at least one DMC compound; b) at least one organic complexing ligand which is not a coronand; and c) at least one coronand. The DMC catalysts of the present invention have increased activity compared to known catalysts.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to double-metal cyanide (DMC) catalystsfor preparing polyether polyols by the polyaddition of alkylene oxideson to starter compounds having active hydrogen atoms.

BACKGROUND OF THE INVENTION

DMC catalysts for the polyaddition of alkylene oxides on to startercompounds having active hydrogen atoms are known. See, for example, U.S.Pat. Nos. 3,404,109; 3,829,505; 3,941,849; and 5,158,922. In comparisonto polyether polyols prepared with alkali catalysts such as, forexample, alkali metal hydroxides, DMC-catalyzed polyether polyolsexhibit a reduction in the content of mono-functional polyethers havingterminal double bonds, so-called “mono-ols”. Polyether polyols preparedwith DMC catalysts can be used to produce high-grade polyurethanes suchas, for example, elastomers, foams and coatings.

DMC catalysts are typically prepared by reacting an aqueous solution ofa metal salt with an aqueous solution of a metal cyanide salt in thepresence of an organic complexing ligand, for example, an ether. In atypical DMC catalyst preparation, aqueous solutions of zinc chloride (inexcess) and potassium hexacyanocobaltate are mixed together to form asuspension. Dimethoxyethane (glyme) is then added to the suspension. TheDMC catalyst is then filtered and washed with an aqueous solution ofglyme. A DMC catalyst prepared in this manner can be represented by thegeneral formula

Zn₃[Co(CN)₆]₂.x ZnCl₂.y H₂O.z glyme

See, for example, EP-A 700 949.

The following references disclose DMC catalysts which use tert-butanolas the organic complexing ligand (by itself or in combination with apolyether) in the preparation of polyether polyols to further reducemono-ol content: JP 4145123; U.S. Pat. No. 5,470,813; EP 700 949; EP 743093; EP 761 708; and WO 97/40086. Additionally, the use of these DMCcatalysts in the production of polyether polyols reduces the inductiontime in the polyaddition reaction of alkylene oxides with correspondingstarter compounds. Catalytic activity also increases with the use ofthese DMC catalysts.

There remains, however, a need for DMC catalysts which have increasedactivity compared to catalysts known in the art which can be used toproduce polyether polyols.

SUMMARY OF THE INVENTION

DMC catalysts of the present invention are composed of: a) at least oneDMC compound; b) at least one organic complexing ligand which is not acoronand; and c) at least one coronand.

DMC catalysts of the present invention have increased activity comparedto catalysts known in the art.

DESCRIPTION OF THE INVENTION

DMC catalysts of the present invention are composed of: a) at least oneDMC compound; b) at least one organic complexing ligand which is not acoronand; and c) at least one coronand.

DMC catalysts of the present invention can optionally comprise water,preferably in an amount from 1 to 10 wt. %, based on the total weight ofthe DMC catalyst. Also, DMC catalysts of the present invention canoptionally comprise one or more water-soluble metal salts, preferably inan amount from 5 to 25 wt. %, based on the total weight of the DMCcatalyst.

Water-soluble metal salts which can be used in the present invention canbe represented by the general formula (I)

M(X)_(n)  (I)

wherein

M is selected from Zn(II); Fe(II); Ni(II); Mn(II); Co(II); Sn(II);Pb(II); Fe(III); Mo(IV); Mo(VI); Al(III); V(V); V(IV); Sr(II); W(IV);W(VI); Cu(II); and Cr(III) (preferably, Zn(II), Fe(II), Co(II) andNi(II));

each X is identical or different, preferably identical, and an anionselected from halides, hydroxides, sulfates, carbonates, cyanates,thiocyanates, isocyanates, isothiocyanates, carboxylates, oxalates andnitrates; and

n is 1, 2 or 3.

DMC compounds of the present invention are the reaction products ofwater-soluble metal salts and water-soluble metal cyanide salts or thecorresponding acids of the metal cyanide salts. Examples ofwater-soluble metal salts which can be used to prepare the DMC compoundsof the present invention can be represented by the general formula (I),in which M is selected from Zn(II); Fe(II); Ni(II); Mn(II); Co(II);Sn(II); Pb(II); Fe(III); Mo(IV); Mo(VI); Al(III); V(V); V(IV); Sr(II);W(IV); W(VI); Cu(II); and Cr(III) (preferably, Zn(II), Fe(II), Co(II)and Ni(II)). Each X is identical or different, preferably identical, andan anion selected from halides, hydroxides, sulfates, carbonates,cyanates, thiocyanates, isocyanates, isothiocyanates, carboxylates,oxalates and nitrates. The value of n is 1, 2 or 3.

Examples of suitable water-soluble metal salts which can be used in thepresent invention include zinc chloride; zinc bromide; zinc acetate;zinc acetylacetonate; zinc benzoate; zinc nitrate; iron(II) sulfate;iron(II) bromide; iron(II) chloride; cobalt(II) chloride; cobalt(II)thiocyanate; nickel(II) chloride; and nickel(II) nitrate. Mixtures ofwater-soluble metal salts can also be used.

Examples of water-soluble metal cyanide salts which can be used toprepare the DMC compounds of the present invention can be represented bythe general formula (II)

(Y)_(a)M′(CN)_(b)(A)_(c)  (II)

wherein

M′ is selected from Fe(II); Fe(III); Co(II); Co(III); Cr(II); Cr(III);Mn(II); Mn(III); Ir(III); Ni(II); Rh(III); Ru(II); V(IV); and V(V)(Co(II), Co(III), Fe(II), Fe(III), Cr(III), Ir(III) and Ni(II) arepreferred) and the water-soluble metal cyanide salt can comprise one ormore of these metals;

each Y is identical or different, preferably identical, and is chosenfrom the group consisting of alkali metal ions and alkaline earth metalions;

A is identical or different, preferably identical, and is chosen fromhalides, hydroxides, sulfates, carbonates, cyanates, thiocyanates,isocyanates, isothiocyanates, carboxylates, oxalates and nitrates; and

a, and b and c are integers, with the values for a, b and c being chosenso that electroneutrality of the metal cyanide salt is achieved (a ispreferably 1, 2, 3 or 4; b is preferably 4, 5 or 6; and c preferably hasthe value 0).

Examples of water-soluble metal cyanide salts which can be used in thepresent invention include potassium hexacyanocobaltate(III); potassiumhexacyanoferrate(II); potassium hexacyanoferrate(III); calcium(hexacyanocobaltate(III); and lithium hexacyanocobaltate(III).

A preferred DMC compound according to the invention can be representedby the general formula (III)

M_(x)[M′_(x′)(CN)_(y)]_(z)  (III)

wherein

M is as defined in formula (I);

M′ is as defined in formula (II); and

x, x′, y and z are integers and are chosen such that electroneutralityof the DMC compound exists.

Preferably,

x=3, x′=1, y=6 and z=2′;

M=Zn(II), Fe(II), Co(II) or Ni(II); and

M′=Co(III), Fe(III), Cr(III) or Ir(III).

Examples of DMC compounds which can be used in the present inventioninclude zinc hexacyanocobaltate(III); zinc hexacyanoiridate(III); zinchexacyanoferrate(III); and cobalt(II) hexacyanocobaltate(III). Furtherexamples of DMC compounds which can be used in the present invention canbe found in, for example, U.S. Pat. No. 5,158,922, the teachings ofwhich are incorporated herein by reference. Zinc hexacyanocobaltate(III)is preferably used in the present invention.

Organic complexing ligands of the present invention are known anddescribed in the following references: U.S. Pat. Nos. 5,470,813;5,158,922; 3,404,109; 3,829,505; and 3,941,849, the teachings of whichare incorporated herein by reference, as well as in EP 700 949; EP 761708; JP 4145123; EP 743 093; and WO 97/40086. Preferably, organiccomplexing ligands of the present invention are water-soluble organiccompounds having heteroatoms such as oxygen, nitrogen, phosphorus orsulfur which are able to form complexes with the DMC compound. Examplesof organic complexing ligands which can be used in the present inventioninclude, for example, alcohols; aldehydes; ketones; ethers; esters;amides; ureas; nitriles; sulfides and mixtures thereof. Preferredorganic complexing ligands are water-soluble aliphatic alcohols such asethanol; isopropanol; n-butanol; iso-butanol; sec.-butanol; andtert.-butanol. Tert.-butanol is particularly preferred.

Suitable coronands which can be used in the present invention includemonocyclic crown compounds such as crown ethers; crown etherssubstituted with heteroatoms (for example, aza-coronands, thia-coronandsor phospha-coronands); spherands; cycles which are composed ofheteroaromatic building blocks such as furans, thiophenes or pyridines(for example, the sexipyridines); and cycles which are composed of ketogroups, carboxylic acid ester groups or carboxylic acid amide groups asdonor sites in the ring (for example, nonactin or valinomycin).Preferably, crown ethers are used. More preferably, crown ethers areused which have a ring system comprising from 3 to 20 oxygen atoms, withtwo adjacent oxygen atoms in each case being linked by a bridge 2 to 6carbon atoms in length. Aliphatic or aromatic rings may be condensed onto the central ring system of the crown ether. The crown ethers may havefunctional groups such as amino groups, hydroxy groups, carboxy groupsor nitro groups.

Examples of un-substituted crown ethers include [12]-crown-4(1,4,7,10-tetraoxacyclododecane); [15]-crown-5(1,4,7,10,13-pentaoxacyclopenta-decane); [18]-crown-6(1,4,7,10,13,16-hexaoxacyclooctadecane); [21]-crown-7(1,4,7,10,13,16,19-heptaoxacyclohenicosane); and [24]-crown-8(1,4,7,10,13,16,19,22-octaoxacyclotetracosane). Examples of crown ethershaving ring systems condensed on to the central ring system includebenzo[15]-crown-5; dibenzo[18]-crown-6; dicyclohexano[18]-crown-6; anddibenzo[30]-crown-10. Examples of crown ethers having additionalfunctional groups include 2-hydroxymethyl[12]-crown-4;2-hydroxymethyl[18]-crown-6; [18]-crown-6-2,3,11,12-tetracarboxylicacid; 4-amino-dibenzo[18]-crown-6; 2-aminomethyl[15]-crown-5;4-formylbenzo[15]-crown-5; 4-nitro-benzo[18]-crown-6; andperfluoro[15]-crown-5. Further examples can be found in 89 J. Chem.Soc., p. 7017 (1967); 84 Angew. Chem. p. 16 (1972); and Gokel et al.,Macrocyclic Polyether Synthesis, (1982).

The amount of DMC compounds present in the DMC catalyst can be from 20to 90 wt. %, preferably, from 25 to 80 wt. %, based on the total weightof the DMC catalyst. The amount of organic complexing ligands present inthe DMC catalyst can be from 0.5 to 30 wt. %, preferably, from 1 to 25wt. %, based on the total weight of the DMC catalyst. The amount ofcoronands present in the DMC catalyst can be from 1 to 80 wt. %,preferably, from 1 to 40 wt. %, based on the total weight of the DMCcatalyst.

DMC catalysts of the present invention can be analyzed by elementalanalysis, thermogravimetric analysis or extractive removal of the ionicsurface-active or interface-active compound content followed bygravimetric determination.

DMC catalysts according to the invention can be crystalline, partiallycrystalline or amorphous. Crystallinity is typically analyzed by powderX-ray diffractometry.

DMC catalysts of the present invention preferably comprise zinchexacyanocobaltate(III), tert.-butanol and coronand

DMC catalysts of the present invention are typically prepared in aqueoussolution by reacting at least one metal salt (preferably represented bythe general formula (I)), with at least one metal cyanide salt(preferably represented by the general formula (II)), in the presence ofat least one organic complexing ligand (which is not a coronand) and atleast one coronand.

In this preparation, in an aqueous solution, the metal salt (forexample, zinc chloride, employed in a stoichiometric excess (at least 50mol. %, based on the molar amount of metal cyanide salt) is reacted withthe metal cyanide salt (for example, potassium hexacyanocobaltate) inthe presence of the organic complexing ligand (for example,tert-butanol). A suspension comprising the DMC catalyst (for example,zinc hexacyanocobaltate), water, excess metal salt and the organiccomplexing ligand is formed.

The organic complexing ligand is either present in the aqueous solutionof the metal salt and/or the metal cyanide salt or is added directly tothe suspension after precipitation of the DMC catalyst. The organiccomplexing ligand is typically used in excess. Preferably, the mixtureof aqueous solution and organic complexing ligand is stirred vigorously.The suspension formed is typically treated with coronands. Coronands arepreferably used in a mixture with water and organic complexing ligand.

The DMC catalyst is isolated from the suspension by known techniquessuch as centrifugation or filtration. In a preferred embodiment of thepresent invention, the isolated DMC catalyst is washed with an aqueoussolution of the organic complexing ligand (for example, by re-suspensionand then renewed isolation by filtration or centrifugation).Water-soluble by-products, for example, potassium chloride, are removedfrom the isolated DMC catalyst by washing with an aqueous solution ofthe organic complexing ligand.

The amount of organic complexing ligand in the aqueous wash solution ispreferably between 20 and 80 wt. %, based on the total weight of theaqueous wash solution. It is advantageous to add coronands to theaqueous wash solution. Preferably, the amount of coronands present inthe aqueous wash solution is from 0.5 to 5 wt. %, based on the totalweight of the aqueous wash solution.

Preferably, the DMC catalyst is washed more than once. This can beaccomplished by repeating the aqueous wash solution procedure describedabove. However, the use of a non-aqueous wash solution for furtherwashing operations is preferred. The non-aqueous wash solution comprisesa mixture of organic complexing ligands and coronands.

The washed DMC catalyst is then dried, optionally, after pulverization,at a temperature between 20-100° C. and under a pressure of between 0.1mbar to normal pressure (1,013 mbar).

The present invention also relates to the preparation of polyetherpolyols by the polyaddition of alkylene oxides on to starter compoundshaving active hydrogen atoms in the presence of the DMC catalysts of thepresent invention.

Examples of alkylene oxides which can be used in the present inventioninclude ethylene oxide, propylene oxide, butylene oxide and mixturesthereof. The build-up of the polyether chains by alkoxylation can beaccomplished by using only one monomeric epoxide, or randomly orblockwise with 2 or 3 different monomeric epoxides. Further details inthis regard can be found in Ullmanns Encyclopädie der industriellenChemie, Volume A21, 1992, p. 670 et seq.

Starter compounds containing active hydrogen atoms which are preferablyused in the present invention are compounds with number averagemolecular weights of 18 to 2,000 with 1 to 8 hydroxyl groups. Examplesof starter compounds useful in the present invention include ethyleneglycol; diethylene glycol; triethylene glycol; 1,2-propylene glycol;1,4-butanediol; hexamethylene glycol; bisphenol A; trimethylolpropane;glycerol; pentaerythritol; sorbitol; sucrose; degraded starch and water.

Starter compounds having active hydrogen atoms, such as have beenprepared, for example, by conventional alkali catalysis from theaforementioned low molecular weight starters and which are oligomericalkoxylation products having number average molecular weights of from200 to 2,000 are preferable used.

The polyaddition of alkylene oxides on to starter compounds havingactive hydrogen atoms, catalyzed by the DMC catalysts of the presentinvention, is typically carried out at temperatures of from 20 to 200°C., preferably, from 40 to 180° C., more preferably, from 50 to 150° C.The reaction can be carried out at total pressures of from 0.0001 to 20bar. The polyaddition can be carried out in bulk or an inert organicsolvent, such as toluene and/or tetrahydrofuran (THF). The amount ofsolvent used is typically from 10 to 30 wt. %, based on the total weightof polyether polyol to be prepared.

The DMC catalyst concentration is chosen such that sufficient control ofthe polyaddition reaction is possible under the given reactionconditions. The catalyst concentration is typically in the range of from0.0005 wt. % to 1 wt. %, preferably, 0.001 wt. % to 0.1 wt. %, morepreferably, 0.001 to 0.0025 wt. %, based on the total weight of thepolyether polyol to be prepared.

The number average molecular weight of the polyether polyol prepared bythe process of the present invention is in the range of from 500 to100,000 g/mol, preferably, 1,000 to 50,000 g/mol, more preferably, 2,000to 20,000 g/mol.

The polyaddition can be carried out continuously or discontinuously,(e.g. in a batch or in semi-batch process).

Due to their increased activity, the DMC catalysts of the presentinvention can be used in low concentrations (25 ppm and less, based onthe amount of the polyether polyol to be prepared). In the preparationof polyurethanes, if a polyether polyol is prepared in the presence ofthe DMC catalyst according to the present invention, the step ofremoving the DMC catalyst from the polyether polyol can be omittedwithout adversely affecting the product quality of the resultingpolyurethane. See Kunststoffhandbuch, Vol. 7, Polyurethane, 3rd Ed.1993, p.25-32 and 57-67.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

EXAMPLES Example 1 Preparation of a DMC Catalyst Comprisingcis-dicyclohexano[18]-crown-6

9 ml of an aqueous 7.4 wt. % potassium hexacyanocobaltate solution wasadded, with vigorous stirring, to a mixture of 15 ml of an aqueous 11.8wt. % zinc chloride solution, 13 ml tert.-butanol and 0.4 gcis-dicyclohexano[18]-crown-6. The precipitate which formed was washedwith a mixture of 10 ml tert.-butanol and 30 ml water and was filteredoff. 20 ml tert.-butanol was then added to the filter residue which wasfiltered again. Following filtration, the catalyst was dried at 50° C.at reduced pressure (10 mbar) to constant weight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=12.9 wt. %; zinc=25.7 wt. %; tert.-butanol=6.0 wt. %;cis-dicyclohexano[18]-crown-6=14.6 wt. %.

Example 2 Preparation of a DMC Catalyst Comprisingcis-dicyclohexano[18]-crown-6

9 ml of an aqueous 7.4 wt. % potassium hexacyanocobaltate solution wasadded, with vigorous stirring, to a mixture of 15 ml of an aqueous 11.8wt. % zinc chloride solution, 13 ml tert.-butanol, 1 ml 12 wt. %ethanoic acid and 0.4 g cis-dicyclohexano[18]-crown-6. The precipitatewhich formed was washed with a mixture of 10 ml tert.-butanol and 30 mlwater and was filtered off. 20 ml tert.-butanol was then added to thefilter residue which was filtered again. Following filtration, thecatalyst was dried at 50° C. at reduced pressure (10 mbar) to constantweight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=10.4 wt. %; zinc=25.3 wt. %; tert.-butanol=4.8 wt. %;cis-dicyclohexano[18]-crown-6=24.2 wt. %.

Example 3 Preparation of a DMC Catalyst Comprisingcis-dicyclohexano[18]-crown-6

26.1 ml of an aqueous 1.84 wt. % hexacyanocobalte acid solution wasadded, with vigorous stirring, to a mixture of 15 ml of an aqueous 11.8wt. % zinc chloride solution, 13 ml tert.-butanol, 1 ml 12 wt. %ethanoic acid and 0.4 g cis-dicyclohexano[18]-crown-6. The precipitatewhich formed was washed with a mixture of 10 ml tert.-butanol and 30 mlwater and was filtered off. 20 ml tert.-butanol was then added to thefilter residue which was filtered again. Following filtration, thecatalyst was dried at 50° C. at reduced pressure (10 mbar) to constantweight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=10.5 wt. %; zinc=19.7 wt. %; tert.-butanol=4.9 wt. %;cis-dicyclohexano[18]-crown-6=15.2 wt. %.

Example 4 DMC Catalyst Comprising cis-dicyclohexano[24]-crown-8

6 ml of an aqueous 7.4 wt. % potassium hexacyanocobaltate solution and 5ml of an aqueous 4.8 wt. % potassium hexacyanoferrate(III) solution wereadded, with vigorous stirring, to a mixture of 15 ml of an aqueous 11.8wt. % zinc chloride solution, 13 ml tert.-butanol and 0.4 gcis-dicyclohexano[24]-crown-8. The precipitate which formed was washedwith a mixture of 10 ml tert.-butanol and 30 ml water and was filteredoff. 20 ml tert.-butanol was then added to the filter residue which wasfiltered again. Following filtration, the catalyst was dried at 50° C.at reduced pressure (10 mbar) to constant weight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=7.3 wt. %; iron=3.7 wt. %; zinc=25.5 wt. %; tert.-butanol=5.2 wt.%; cis-dicyclohexano[24]-crown-8=21.7 wt. %.

Example 5 DMC Catalyst Comprising cis-dicyclohexano[18]-crown-6

4.5 ml of an aqueous 7.4 wt. % potassium hexacyanocobaltate solution and5 ml of an aqueous 7.2 wt. % potassium hexacyanoferrate(III) solutionwere added, with vigorous stirring, to a mixture of 15 ml of an aqueous11.8 wt. % zinc chloride solution, 13 ml tert.-butanol and 0.4 gcis-dicyclohexano[18]-crown-6. The precipitate which formed was washedwith 30 ml water and was filtered off. 20 ml tert.-butanol was thenadded to the filter residue which was filtered again. Followingfiltration, the catalyst was dried at 50° C. at reduced pressure (10mbar) to constant weight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=6.2 wt. %; zinc=25.9 wt. %; iron=5.9 wt. %; tert.-butanol=5.9 wt.%; cis-dicyclohexano[18]-crown-6=16.7 wt. %.

Example 6 Preparation of a DMC Catalyst Comprising [18]-crown-6

9 ml of an aqueous 7.4 wt. % potassium hexacyanocobaltate solution wasadded, with vigorous stirring, to a mixture of 28 ml of an aqueous 12.7wt. % zinc chloride solution, 13 ml tert.-butanol, 1 ml 12 wt. %ethanoic acid and 0.4 g [18]-crown-6. The precipitate which formed waswashed with 30 ml water and was filtered off. 20 ml tert.-butanol wasthen added to the filter residue which was filtered again. Followingfiltration, the catalyst was dried at 100° C. at reduced pressure (10mbar) to constant weight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=11.0 wt. %; zinc=26.2 wt. %; tert.-butanol=6.2 wt. %;[18]-crown-6=15.1 wt. %.

Example 7 Preparation of a DMC Catalyst Comprising [15]-crown-5

27 ml of an aqueous 1.79 wt. % hexacyanocobalte acid solution was added,with vigorous stirring, to a mixture of 28 ml of an aqueous 12.7 wt. %zinc chloride solution, 13 ml tert.-butanol, 1 ml 12 wt. % ethanoic acidand 0.4 g [15]-crown-5. The precipitate which formed was washed with 30ml water and was filtered off. 20 ml tert.-butanol was then added to thefilter residue which was filtered again. Following filtration, thecatalyst was dried at 100° C. at reduced pressure (10 mbar) to constantweight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=10.7 wt. %; zinc=23.3 wt. %; tert.-butanol=5.0 wt. %;[15]-crown-5=11.4wt. %.

Example 8 Preparation of a DMC Catalyst Comprising2-hydroxymethyl[18]-crown-6

9 ml of an aqueous 7.4 wt. % potassium hexacyanocobaltate solution wasadded, with vigorous stirring, to a mixture of 14 ml of an aqueous 12.7wt. % zinc chloride solution, 13 ml tert.-butanol and 0.4 g2-hydroxymethyl[18]-crown-6. The precipitate which formed was washedwith 30 ml water and was filtered off. 20 ml tert.-butanol was thenadded to the filter residue which was filtered again. Followingfiltration, the catalyst was dried at 100° C. at reduced pressure (10mbar) to constant weight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=10.4 wt. %; zinc=24.7 wt. %; tert.-butanol=5.8 wt. %;2-hydroxymethyl[18]-crown-6=12.4 wt. %.

Example 9 DMC Catalyst Comprising 2-hydroxymethyl[18]-crown-6

27 ml of an aqueous 1.79 wt. % hexacyanocobalte acid solution was added,with vigorous stirring, to a mixture of 14 ml of an aqueous 12.7 wt. %zinc chloride solution, 13 ml tert.-butanol, 1 ml 12 wt. % ethanoic acidand 0.4 g 2-hydroxymethyl[18]-crown-6. The precipitate which formed waswashed with 30 ml water and was filtered off. 20 ml tert.-butanol wasthen added to the filter residue which was filtered again. Followingfiltration, the catalyst was dried at 100° C. at reduced pressure (10mbar) to constant weight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=10.1 wt. %; zinc=20.2 wt. %; tert.-butanol=4.2 wt. %;2-hydroxymethyl[18]-crown-6=13.4 wt. %.

Comparative Example 10 Preparation of a DMC Catalyst Which Does NotComprise a Coronand

9 ml of an aqueous 7.4 wt. % potassium hexacyanocobaltate solution wasadded, with vigorous stirring, to a mixture of 15 ml of an aqueous 11.8wt. % zinc chloride solution and 13 ml tert.-butanol. The precipitatewhich formed was washed with 10 ml tert.-butanol and was filtered off.20 ml tert.-butanol was then added to the filter residue which wasfiltered again. Following filtration, the catalyst was dried at 50° C.at reduced pressure (10 mbar) to constant weight.

Elemental analysis, thermogravimetric analysis and extraction:cobalt=15.7 wt. %; zinc=27.8 wt. %; tert.-butanol=7.9 wt %.

Preparation of Polyether Polyols General Method

To determine the activity of the catalysts prepared in the presentinvention, 50 g polypropylene glycol starter (molecular weight=1000g/mol) and 20 mg catalyst were introduced under protective gas (argon)into a 500 ml pressure reactor and heated to 130° C. while stirring.

Within 30 minutes, a maximum of 50 g propylene oxide was dispensed-in ata pressure of 2.5 bar. After 30 minutes, the reaction mixture was cooledto room temperature and propylene oxide was removed by purging withargon.

The product was characterized by a molecular weight distribution (weightaverage) determined by gel permeation chromatography (GPC).

The results which were obtained are illustrated in Table 1.

TABLE 1 Molecular Weight Distribution of the Catalysts Prepared inExamples 1-10: Catalyst of Example No. M_(w) [g/mol] 1 2130 2 1970 31940 4 2180 5 2020 6 1920 7 1890 8 1910 9 1900 10 (Comparison) 1310

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A double-metal cyanide catalyst comprising: a) atleast one double-metal cyanide compound; b) at least one organiccomplexing ligand which is not a coronand; and c) at least one coronand.2. The double-metal cyanide catalyst of claim 1, further comprisingwater and/or at least one water-soluble metal salt.
 3. The double-metalcyanide catalyst of claim 1 in which the double-metal cyanide compoundis zinc hexacyanocobaltate (III).
 4. The double-metal cyanide catalystof claim 1 in which the organic complexing ligand is an alcohol,aldehyde, ketone, ether, ester, amide, urea, nitrile, sulfide and/or amixture thereof.
 5. The double-metal cyanide catalyst of claim 1 inwhich the organic complexing ligand is tert.-butanol.
 6. Thedouble-metal cyanide catalyst of claim 1 in which the amount of coronandpresent in the double-metal cyanide catalyst is from about 1 to about 80wt. %, based on the total weight of the double-metal cyanide catalyst.7. A process for preparing the double-metal cyanide catalyst of claim 1,comprising: (a) reacting, in aqueous solution, (i) at least one metalsalt, (ii) with at least one metal cyanide salt or the correspondingacid of the metal cyanide salt, in the presence of (iii) at least oneorganic complexing ligand which is not a coronand, to form a suspension;and (b) treating the suspension with at least one coronand.
 8. Theprocess of claim 7, further comprising: (c) isolating the double-metalcyanide catalyst from the suspension; and (d) washing the double-metalcyanide catalyst; and (e) drying the double-metal cyanide catalyst.
 9. Aprocess for preparing a polyether polyol by the polyaddition of analkylene oxide onto a starter compound having active hydrogen atoms inthe presence of a catalyst, the improvement wherein the catalystcomprises the double-metal cyanide catalyst of claim 1.